1. Field of the Invention
The present invention relates to data processing technology, and more specifically, to a technology of decoding coded data.
2. Description of Related Art
In the digital transmission system, in order to secure reliability of data transmitted and received, the error correcting code and the error detecting code are used. FIG. 16 is a schematic diagram that outlines a digital transmission system in which an error correcting code and an error detecting code are used.
As shown in FIG. 16, the transmitting side performs error detection coding and error correction coding on the data that is intended to be transmitted to the opposite party (transmission data), subsequently modulates it to obtain the modulated coded data, and outputs it into a communication channel. In the communication channel, there is a possibility that a noise leading to an error may mix with this data.
A receiving side demodulates the received data to obtain the coded data and decodes this coded data. The receiving side performs error correcting in the decoding, and performs error detection on decoded data obtained by the decoding. Usually, when the error correction is incomplete as a result of the error detection, the receiving side requires the transmitting side to retransmit the data.
If errors are detected frequently, then many retransmissions will also occur and efficiency of the communication system will fall. Especially, in mobile communication systems, since the intensity of a radio wave varies substantially due to influences of fading etc. and noise is easy to mix, this problem is salient. Therefore, the receiving side is required to have a high correction capability.
Patent Document (Japanese Unexamined Patent Application Publication No. 2006-345080) discloses a technique of improving an error correction capability. FIG. 17 and FIG. 18 correspond to FIG. 1 and FIG. 2 in the Patent Document, respectively; FIG. 16 shows a receiver set to which the technique of the Patent Document is applied; and FIG. 17 is a flowchart showing a flow of processing by the receiver set.
In the receiver set shown in FIG. 16, an antenna unit 11 receives a frame via a network, and a demodulator unit 12 demodulates the received frame (S11). An error correction unit 13 performs an error correction processing on the frame after the demodulation. In the error correction unit 13, for example, Reed-Solomon decoding and further Viterbi decoding are performed.
The error detection unit 14 performs an error detection processing based on an error detecting code included in the frame after the error correction processing (S12, S13). The error detecting code is, for example, CRC (Cyclic Redundancy Check).
The error correction unit 15 performs an error correction processing on the frame from which the error was detected in the error detection unit 14 (S14: Yes, S15: Yes, S16). This error correction processing replaces a portion of the frame using the known information acquired in advance. For example, a transmitter address included in the frame from which an error was detected and the like are replaced with a terminal address in the same network acquired in advance.
After that, the error detection unit 14 and the error correction unit 15 repeat processings of Steps S13 to S16 plural times until the error disappears in the frame (S13, S14: Yes, S15, S16, S13, . . . ). Moreover, when the error still exits but a predetermined terminating condition is fulfilled (S15: No), the retransmission control unit 16 performs a retransmission control (S17). In the retransmission control, for example, the retransmission control unit 16 makes the transmitting side retransmit the frame by not returning the ACK (Acknowledgement) frame for the received frame.
In this way, the technique disclosed by the Patent Document enhances the error correction capability by repeatedly performing a process whereby a part of a field of the frame in which an error was detected is replaced with known information that is normal data and the error detection processing is performed again on the frame after the substitution, and as a result, controls a detection frequency of errors or the number of times of retransmission.